1. Technical Field
The present invention generally relates to flexible fueled vehicles and, more particularly, to a method for determining the integrity of a fuel composition sensor in the flexible fueled vehicle.
2. Discussion
A flexible fueled vehicle is a vehicle which is capable of operating on different fuels such as gasoline, alcohol, or any mixture of the two. Modifications to the operating parameters of an engine are necessary when operating on different fuels due to the different combustion characteristics of each fuel. For example, an engine operating on a fuel including a high percentage of alcohol requires a greater ratio of fuel-to-air as compared to an engine operating on a fuel including a high percentage of gasoline. If the fuel-to-air ratio is set incorrectly (i.e., non-stoichiometric), perfect combustion cannot be achieved. This may lead to rough engine operation and/or poor emissions.
Flexible fueled vehicles are often equipped with a fuel composition sensor for determining the nature of the particular fuel mixture delivered to the engine. The fuel composition sensor is disposed along a fuel line and senses select characteristic of the fuel which indicates the concentration of alcohol (i.e., optical, conductivity, capacitive, etc.) of the fluid passing thereby. In response, the fuel composition sensor generates a voltage signal indicative of the particular fuel mixture being delivered to the engine. The voltage signal is sent to the engine control system which sets the fuel-to-air ratio for the engine in accordance therewith.
Unfortunately, modern flexible fueled vehicles do not incorporate a mechanism for detecting a malfunctioning fuel composition sensor. As such, the engine control system may set an improper fuel-to-air ratio for the engine based on the voltage signal from the malfunctioning fuel composition sensor. This could cause rough engine operation, poor emissions, and/or engine damage.
In view of the foregoing, there is a need in the art for a control system for monitoring the functioning of a fuel composition sensor such that malfunctions may be detected.
The above and other objects are provided by a method for determining the integrity of a fuel composition sensor. The method includes testing the fuel composition sensor at an ignition on event for electrical and rational integrity. The electrical check determines whether the fuel composition sensor voltage is shorted high or shorted low, and also tests for electrical continuity. The rational check determines whether the voltage signal from the fuel composition sensor at the ignition-on event is within a calibratible threshold of the last voltage signal received from the fuel composition sensor before the previous ignition-off event. If the fuel composition sensor fails either the ignition-on electrical or rational checks, a fault code is set and the engine control system converts to a fuel composition sensor limp-in mode.
If the fuel composition sensor passes the ignition-on electrical and rational checks, the engine control system operates in a normal mode employing the output signal from the fuel composition sensor as a basis for setting the fuel-to-air ratio for the engine. During normal operation, the fuel composition sensor is periodically tested for potential rationality malfunctions. These periodic rationality tests are non-intrusive in nature and do not set a fault code by themselves but only enable a second, intrusive-type, check. The non-intrusive testing includes three different determinations.
The first non-intrusive check is triggered when the fuel level increases greater than a fuel volume added threshold. Upon this occurrence, the fuel composition sensor output value is compared to two projected fuel composition possibilities. This check assumes that either a low or high concentration of alcohol based fuel was added to the fuel tank. If the fuel composition sensor output value differs by more than a calibratible amount from the two projected fuel composition possibilities, a flag is set for the engine control system to conduct additional, intrusive-type, testing.
The second non-intrusive check of the fuel composition sensor continuously monitors the system for an unexpected shift in the amount of fuel delivered to the engine. If the amount of fuel delivered varies more than a calibratible amount, as compared to nominal operating conditions, a flag is set for the engine control system to conduct additional, intrusive-type, testing.
The third non-intrusive check of the fuel composition sensor involves continuously monitoring the fuel composition sensor""s output for a significant deviation from a previously stored, fully updated, fuel composition sensor output value in the absence of a fuel fill trigger. If the current fuel composition sensor output value is more than a calibratible difference from the stored, fully updated fuel composition sensor value, a flag is set for the engine control system to conduct additional, intrusive-type, testing.
Upon the failure of any of the three non-intrusive checks, intrusive testing is conducted. The intrusive testing involves learning the composition of the fuel by way of the vehicle""s exhaust gas oxygen sensor feedback system. The fuel composition determined by the exhaust gas oxygen sensor feedback system is compared to the fuel composition sensor output value. If the difference between the two values is greater than a predetermined threshold, the engine control system converts to a limp-in mode. In the limp-in mode, the exhaust gas oxygen sensor feedback system is used to determine the composition of the fuel and the fuel-to-air ratio for the engine is set in accordance therewith.